The present invention is in the field of reducing drag on land operated vehicles, and pertains particularly to a system for channeling air to reduce frictional drag and to form a bug guard from the channeled and directed airflow.
The art of aerodynamic design is one of continual change and improvement. In addition to streamline profiling of surfaces belonging to aerodynamic vehicles of ground, air and water types, a number of aerodynamic aids have been provided in the form of accessories that may be attached to vehicles at strategic locations with the idea of reducing drag on those vehicles. Air-foils of various designs are the most recognized of these products.
With respect to road transport vehicles such as semi tractor trailers and the like, the bluff profile inherent with such vehicles causes more drag when moving through air than with streamlined profiles that are not practical in production of such vehicles. Therefore, a large market exists for ways to reduce drag on such bluff-bodied vehicles to improve fuel use when the equipped vehicles are driven at certain speeds.
Aerodynamic drag on bluff-bodied vehicles consists mainly of pressure drag with skin friction created by moving air and base drag, which forms part of the total drag coefficient on the vehicle. Air-flow over bluff bodies comprises large wake production and smaller vortex shedding. The well-known Reynolds number associated with drag on small and medium vehicles falls in the sub-critical range of (1.0 to 2.0xc3x97106). Total drag force associated with such typical flow patterns is very high. A considerable amount of energy is therefore expended in overcoming such forces.
Streamlining vehicle designs is one of the most popular known methods for reducing aerodynamic drag. The effectiveness of rounding corners in design can be measured by utilizing a simple two-dimensional square section under test. The drag coefficient on such a square section at sub-critical Reynolds numbers is approximately 2.0. Maximally rounded corners improve the coefficient to a limiting factor of approximately 1.0 or a 50% reduction in drag without major design change.
Small vortex generators are known in the art, and are used in typically small aircraft to increase lift. Referring now to FIG. 1 of this specification, a vortex generator is illustrated in perspective view. Generator 100 has a base portion 101 that makes contact with the surface of a vehicle to which it is mounted and a fin portion 102 formed at a substantially upright direction from the base of the unit.
Typically, an array of such generators are arranged on a leading-edge surface of an aircraft wing to increase lift. Referring now to FIGS. 2a, 2b, and 2c, the generator of FIG. 1 is illustrated in Top, Side, and End views to better show construction. In FIGS. 2a and 2c, part of fin 102 is shown removed along an angle D for the purpose of further drag reduction in the design. Dimensions B (FIG. 2a), C (FIG. 2b) and E (FIG. 2c) can vary according to application.
An object of the present invention is to reduce drag and to increase fuel efficiency of a bluff-body vehicle through strategic alignment and positioning of vortex generators at leading edges of the vehicle. A further object of the present invention is to use the laminar flow enhanced by added vortex generators to circumvent a common problem of bug collision with windshields of such vehicles while traveling at freeway speeds.
In a preferred embodiment of the present invention an aerodynamic bug diversion system for creating and directing an airflow shield to prevent bugs and other lightweight debris from hitting the windshield of a moving vehicle is provided, comprising an array of vortex generators affixed in a line substantially at a right angle to the direction of vehicle travel at a leading edge of the vehicle for creating a channeled and uniform laminar airflow, and an airfoil having at least 2 foils held spaced apart and substantially parallel to one another for collecting and redirecting the airflow created by the vortex array. The system is characterized in that the airflow through the airfoil is redirected as a substantially flat and uniform flow traveling upward in a plane substantially parallel to the plane of the windshield providing a divertive shield against bugs and debris hitting the windshield.
In some embodiments the airfoil is formed of one polymer piece in a molding operation. In other embodiments the airfoil may be formed of 2 or more polymer pieces and is assembled. In some cases the at least two foils are held spaced apart by a plurality of support fins, the fins aiding in channeling the air flow. Various materials can be used, such as aluminum.
In some embodiments the airfoil can be adjustable to a specific profile, adjusting one or both of the spacing and the direction.
In another aspect of the invention an airfoil for directing an airflow shield to prevent bugs and other lightweight debris from hitting the windshield of a moving vehicle is provided, comprising a base foil having a forward protruding lip for collecting incoming airflow and an upright curvature substantially following the angle of protrusion of the windshield from the vehicle, and an upper foil connected to and spaced-apart from the base foil at a position elevated from and substantially parallel to the base foil. The airfoil is characterized in that the space between the base foil and the upper foil functions to redirect airflow in a path substantially parallel to the windshield, forming a bug shield of moving air.
In some cases the upper foil is held rigidly above the base foil by a plurality of support fins, the fins aiding in channeling the airflow. The apparatus can be formed of one polymer piece in a molding operation, of two or more pieces. Various materials can be used, such as aluminum. The airfoil may be adjustable in one or both of direction and/or spacing. Further, there may be two or windshield support feet adapted as standoffs to the windshield.
In another aspect of the invention a method for preventing bugs and other lightweight debris from hitting the windshield of a vehicle is provided, comprising steps of (a) collecting an incoming airflow in an airfoil having at least an upper foil and a base foil while the vehicle is in motion; and (b) redirecting the captured airflow through the airfoil in an upward direction substantially parallel to the windshield.
In some embodiments, in step (a), the incoming airflow is channeled, prior to the airfoil, through an array of vortex generators. The airfoil may be a contiguous piece formed in a molding operation, or may be made of two or more pieces that are assembled together.
In some cases the airfoil is adjustable in one or both of spacing and direction. Also in some cases the foils comprising the airfoil are held apart by a plurality of support fins, the fins aiding in channeling the air flow created by the vortex array. Redirection in preferred embodiments is accomplished through curvatures formed in the airfoil.
In yet another aspect of the invention a system for reducing drag on a land-operating vehicle, and therefore increasing fuel efficiency is provided, comprising an array of vortex generators, each presenting a substantially vertical foil to an airstream created by driving the vehicle through ambient air, the array affixed to a surface of the vehicle and extending substantially in a line at a right angle to the direction of vehicle travel, the system reducing turbulence and enhancing laminar flow.
In some embodiments the line of generators is imposed along a forward position on a hood of the vehicle. In other embodiments the line of generators is imposed along a forward position on a cab top of the vehicle. In yet other embodiments a first line of generators imposed along a forward position on a cab top of the vehicle, and a second line of generators along a forward position of a hood of the vehicle. The individual generators may be aligned to spread the laminar flow created to a width greater than the width of the line of generators.
In embodiments of the invention taught below in enabling detail, for the first time a system is provided wherein vortex generators are used to reduce drag and thusly lower operating costs for land vehicles, such as trucks and buses. In addition, a system is provided that eliminates bug impingement on windshields of such vehicles, and the bug system can be used with the vortex generators as well.